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IEEE Std 802.3-2015
IEEE Standard for Ethernet
SECTION THREE
20
Copyright © 2016 IEEE. All rights reserved.
35.1.1 Summary of major concepts
a) The GMII is based on the MII defined in Clause 22.
b) Each direction of data transfer is serviced by Dat
a (an eight-bit bundle), Delimiter, Error, and Clock
signals.
c) Two media status signals are provided. One indica
tes the presence of carrier, and the other indicates
the occurrence of a collision.
d) The GMII uses the MII management interface composed
of two signals that provide access to man-
agement parameters and services as specified in Clause 22.
e) MII signal names have been retained and the functi
ons of most signals are the same, but additional
valid combinations of signals have been defined for 1000 Mb/s operation.
f) The Reconciliation sublayer maps the
signal set provided at the GMII to the PLS service primitives
provided to the MAC.
g) GMII signals are defined such that an implementat
ion may multiplex most GMII signals with the
similar PMA service interface defined in Clause 36.
h) The GMII may also support Low Power Idle (LPI) sign
aling as defined for Energy-Efficient Ether-
net in Clause 78 for certain PHY types.
35.1.2 Application
This clause applies to the interface between the MAC and
PHYs, and between PHYs and Station Management
entities. The implementation of the interface is primarily intended as a chip-to-chip (integrated circuit to
integrated circuit) interface implemented with traces on a printed circuit board. A motherboard-to-daughterboard
interface between two or more printed circuit boards is not precluded. The use of parts of the GMII (e.g., data
paths, but not the Clause 22 management interface or associated management register
s), and the use of the GMII
as an interface between logic modules on th
e same chip is not precluded.
This interface is used to provide media independence so t
hat an identical media access controller may be used
with any of the copper and optical PHY types.
35.1.3 Rate of operation
The GMII supports only 1000 Mb/s operation and is defined
within this clause. Operation at 10 Mb/s and 100
Mb/s is supported by the MII defined in Clause 22.
PHYs that provide a GMII shall support 1000 Mb/s operatio
n, and may support additional rates using other
interfaces (e.g., MII). PHYs must report the rates at which they are capable of operating via the management
interface. Reconciliation sublayers that provide a GMII shall support 1000 Mb/s and may support additional
rates using other interfaces.
35.1.4 Allocation of functions
The allocation of functions at the GMII balances the need
for media independence with the need for a simple and
cost-effective interface.
While the Attachment Unit Interface (AUI) was defined t
o exist between the Physical Signaling (PLS) and
Physical Medium Attachment (PMA) sublayers for 10 Mb/s DTEs, the GMII (like the Clause 22 MII)
maximizes media independence by cleanly separatin
g the Data Link and Physical Layers of the ISO/IEC seven-
layer reference model. This allocation also recognizes that implementations can benefit from a close coupling
between the PLS or PCS sublayer and the PMA sublayer.